Phosphorylation Dependent Sequestration Of Protein Phosphatase-1 _I (PP-1 _I) By Protein 14-3-3

PP-1 is involved in the control of the meiotic and mitotic cell divisions at the G2 to M transition by dephosphorylating phospho-serine 217 (phospho-serine 287 in Xenopus) of Cdc25, accompanied by activation of Cdc25 which would then dephosphorylate and activate Cdk1 . PP-1I has been proposed to be the form of PP-1 that dephosphorylates and activates Cdc25. Here we show that PP-1I is sequestered in a phosphorylation dependent manner by protein 14-3-3 involving phosphorylation of serine 71 of I-2 moiety of PP-1I by C-TAK1. Phosphorylation of serine 71 of the I-2 moiety of PP-1I by C-TAK1 enhanced the sequestration and inhibition of PP-1I by Protein 14-3-3. Phosphorylation of serine 71 of the I-2 moiety of PP-1I caused an increase in the Stability Energy, Binding Energy of the interaction between PP-1I and Protein 14-3-3 and a significant decrease in the IC50 of the inhibition of PP-1I by Protein 14-3-3. PP-1I regulation by C-TAK1 and Protein 14-3-3 is a mechanism for the control of Cdc25 at the G2 to M transition of the cell cycle.